<p>Exceptions are meant to represent the application's state at which an error occurred.</p>
<p>Making all fields final ensures that this state:</p>
<ul>
<li> Will be fully defined at the same time the exception is instantiated.</li>
<li> Won't be updated or corrupted by some bogus error handler.</li>
</ul>
<p>This will enable developers to quickly understand what went wrong.</p>
<p>The following code:</p>
<pre>
public class MyException extends Exception {

  private int status;                               // Noncompliant

  public MyException(String message) {
    super(message);
  }

  public int getStatus() {
    return status;
  }

  public void setStatus(int status) {
    this.status = status;
  }

}
</pre>
<p>should be refactored into:</p>
<pre>
public class MyException extends Exception {

  private final int status;                         // Compliant

  public MyException(String message, int status) {
    super(message);
    this.status = status;
  }

  public int getStatus() {
    return status;
  }

}
</pre>

